1. Field of the Invention
The present invention relates to a projection-type image display apparatus.
2. Description of the Related Art
A white light source, such as a mercury vapor lamp, is used as a light source in conventional projection-type image display apparatus. To create a full-color image by using a white light emitted from a white light source, it is necessary to separate the white light into different color components, such as red, green, and blue light components by using an optical color separation filter. In recent years, however, a plurality of single-color semiconductor lasers is used in place of a white light source. Use of the plurality of single-color semiconductor lasers enables formation of a full-color image without using an optical color separation filter.
However, when a plurality of single-color lasers are used, an output light intensity of a laser beam emitted from each of the single-color semiconductor lasers can be non-uniform. Moreover, a temporal change of the output light intensity can be non-uniform. To obtain a uniform output from each of the plurality of single-color lasers, it is necessary to perform output control of the single-color semiconductor lasers. However, because this control is typically performed based on light intensities or chromaticities of the laser beams, it is necessary to detect the light intensities or chromaticities.
Japanese Patent Application Laid-open No. 2005-331906 discloses a detecting device that detects a light intensity of a projected image. The projected image is created by using a combined light obtained by combining a plurality of laser light sources and directing the combined light onto an image plane. In this way, the detecting device detects light intensity distribution on the image plane. Subsequently, the laser light sources and an optical system are adjusted based on the detected light intensity distribution. In this manner, the non-uniformity of light intensities of the projected image can be suppressed.
To create an image having a desired chromaticity, or a desired light intensity, it is necessary to detect a chromaticity, or a light intensity, of the combined light in which each component is combined uniformly. However, the detecting device disclosed in Japanese Patent Application Laid-open No. 2005-331906 cannot necessarily detect a combined light in which each component is combined uniformly; because, the detecting device detects a light intensity of the projected image. It may happen that the detecting device detects a combined light having only a color component corresponding to a certain laser light source. Therefore, there is a possibility that the light intensity cannot be detected accurately.
The output power of each laser light source gradually changes with time and each laser light source has a different change ratio. Therefore, a ratio of light intensities of laser beams emitted from the laser light sources varies with time. This can lead to create a projected image of which white balance is not constant. Furthermore, it is not possible to detect whether light emitted from a laser light source has been blocked or is leaking out of its optical path when a failure occurs on a component in the projection-type image display apparatus.